Enzyme inhibition

Inhibitors Inhibitors are chemicals that reduce the rate of

enzymic reactions The are usually specific and they work at low

concentrations They block the enzyme but they do not

usually destroy it Many drugs and poisons are inhibitors of

enzymes in the nervous system

© 2008 Paul Billiet ODWS

http://www.saburchill.com/IBbiology/bio_hp.html

The effect of enzyme inhibition Reversible inhibitors:

The effects are temporary and when inhibitor is removed enzyme regains full activity.

There are two types :


1. Competitive: These compete with the substrate molecules for the active site

Increasing substrate concentration will reduce effects of inhibitor

Resembles the substrate’s structure closely

Enzyme inhibitor complex

Reversible reaction

E + I EI


The effect of enzyme inhibition

Succinate Fumarate + 2H++ 2e-

Succinate dehydrogenase

CH2COOH

CH2COOH CHCOOH

CHCOOH

COOH

COOH

CH2

Malonate


2. Non-competitive: These are not influenced by the concentration of the substrate. It inhibits by binding irreversibly to the enzyme but not at the active site

They alter the overall shape of the enzyme.

Examples Cyanide combines with the Iron in the enzymes

cytochrome oxidase Heavy metals, Ag or Hg, combine with –SH groups.


Graph

Irreversible inhibitors: Combine with the functional groups of the amino acids in the active site, irreversibly

Examples:

Cyanide is a non reversible inhibitor of cytochrome oxidase


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Enzyme inhibition